The present invention relates to an apparatus for manipulating in the height and in particular setting down of a load. The invention relates particularly, though not exclusively, to an apparatus for placing or setting down an element which is heavy but highly susceptible to damage, such as a coupling tube in a tube column, wherein after drilling to a depth corresponding with the length of the coupling tube a new coupling tube is added to the drill column. This is the case for instance in the extraction of oil and natural gas.
The screw thread connections with sealing surfaces between separate coupling tubes in the tube column are very susceptible to damage when a coupling tube is lowered with too great a force onto the already formed tube column. A damaged coupling tube, or of which at least the screw thread connection, which is often a conical screw thread connection, or a sealing surface is damaged, is written off and cannot be used. Such coupling tubes often weight 600 kg, although their weight varies considerably from tube to tube.
Apparatuses are known in the art for height manipulation of such loads. These known apparatuses have the drawback that they need precise information in advance concerning the actual weight of a load for manipulating before manipulation of this load can take place. The changing or in any case adjusting of a setting is required for this purpose. If this is not done, the load may be set down with too great a force and suffer damage.
The known apparatuses also have other drawbacks in addition to this above described lack of sensitivity. The weight of a load for manipulating is often very great, particularly in relation to the desired sensitivity during manipulation and in particular during setting down of the load. For this relation between great weight and fine sensitivity no solution has yet been found in the known art.
The present invention has for its object to obviate or at least mitigate the problems and shortcoming of the known apparatuses, for which purpose an apparatus according to the present invention is distinguished by a suspension on a lifting device, which suspension comprises a drive, with which drive the load can be manipulated in the height; a weighing device with which the weight of the load can be determined; a linear hydraulic accumulator serving as a xe2x80x9cmemoryxe2x80x9d connected to the weighing device for storing an initial weight of the load; comparing means for comparing an actual weight with the initial weight stored in the memory for the purpose of selective energizing of the drive in response to the comparison.
An apparatus according to the invention is capable of manipulating heavy loads very delicately and has no problems, within the operational range of course, with the variation in weight of the individual loads for manipulating.
In one embodiment the weighing device comprises a hydraulic weighing cylinder and the hydraulic accumulator is at least approximately linear in a range of operating pressures. A fully mechanical/hydraulic operation of the weighing cylinder and the accumulator is thus achieved without precise determination of the actual weight of the load, but in the form of pressure storage as a reference value corresponding to this weight.
It is noted that in such an embodiment the hydraulic accumulator can very advantageously be designed as a hydraulic hose of a determined length, because this will behave, depending on the chosen length thereof, the chosen or used type of hose, in linear manner in said range of operating pressure, or will do so at least approximately.
In order to ensure a xe2x80x9cmemoryxe2x80x9d operation of the hydraulic accumulator, i.e. the entrapped pressure serving as a reference value, a closing valve can be arranged in an embodiment of the invention in a line between the weighing cylinder and the hydraulic accumulator. The closing valve is opened in order to determine the initial value, wherein an open connection is effected be between the weighing cylinder, the line and the hydraulic accumulator, whereafter the closing valve can be closed. The hydraulic accumulator now retains the initial pressure value as xe2x80x9cmemoryxe2x80x9d which can thus be used for comparison with weights of the load actually borne by the weighing cylinder.
In another embodiment of the invention the comparing means can be formed by a control valve connected on one side to the weighing device and on the other to the memory. In the latterly described embodiment of a weighing cylinder as hydraulic design for the weighing device and a hydraulic accumulator as design for the memory, the actuators of the control valve can be hydraulic and directly connected to respectively the weighing cylinder and the accumulator. A very simple and reliable mechanical/hydraulic configuration is hereby also obtained. The above stated closing valve can herein be arranged in parallel over the control valve in the line between the weighing cylinder and the accumulator.
In the above stated embodiment with hydraulic actuators of a control valve etc., the control valve can comprise a control piston enclosed on both sides between flexible membranes in a control cylinder, and the actuators can be open connections to respectively the weighing cylinder and the accumulator which act on the membranes, wherein the drive can be energized subject to pressure differences over the control valve and connections for opening herein. In the configuration of the control valve with membranes which enclose the actual control valve in flexible manner, very controlled movements of the control valve in the control cylinder are possible without the very abrupt connection transitions usual in the known art. So-called xe2x80x9covershootxe2x80x9d problems are hereby prevented and a very controlled operation of the drive is realized.
A further embodiment has the feature that the accumulator is adapted to retain therein a weight decreased by a predetermined quantity. A downward movement caused by the drive is hereby ensured, independently of a separate crude movement mechanism which can remain limited to the function of movement over large distances, wherein the drive according to the invention takes over displacement. In an embodiment with a hydraulic weighing cylinder and a hydraulic accumulator, a pressure amplifier can be connected to the accumulator. The desired decrease in the weight to be retained as a reference can then be adjusted therewith, thereby serving as a memory feature. The predetermined quantity by which the weight is to be decreased preferably corresponds to a desired and/or allowable contact force during moving or setting down of the load. Herein the desired or allowable contact force is with certainty not exceeded.
Further embodiments are defined in the dependent claims and comprise a hybrid system of hydraulics and pneumatics, a drive designed as double-action hydraulic cylinder connected to at least one hydraulic source of medium under pressure or the like, etc.